Hand-held machine tool comprising a sealing ring disposed in the tool holder

ABSTRACT

A low-wear sealing ring, which assures a favorable sealing action that prevents the escape of lubricants from the transmission chamber of the machine tool and prevents the entry of dust into the transmission chamber, has a number of sealing lips ( 6, 7 ) that rest against a percussion bolt ( 3 ) in the machine tool. At least on its lateral flank oriented toward the machine, the sealing ring ( 4 ) is provided with one or more radially extending recesses ( 8, 9 ). This lends the sealing lips ( 6, 7 ) a high degree of flexibility, allowing them to easily follow the movements of the percussion bolt ( 3 ), as a result of which the sealing ring ( 4 ) has a low susceptibility to wear and assures a high degree of impermeability.

PRIOR ART

[0001] The current invention relates to a hand power tool with a toolholder, which can be driven in a rotary and percussive fashion and inwhich a percussion bolt is supported so that it can move axially, inwhich the tool holder contains at least one sealing ring thatencompasses the percussion bolt.

[0002] DE 197 24 532 A1 has disclosed a drilling and hammering machinetool of this kind. The percussion bolt must be sealed in relation to thetool holder in such a way that on the one hand, no lubricant escapesfrom the transmission chamber of the machine tool and on the other hand,no dirt from the outside gets into the transmission chamber of themachine through the tool holder. To that end, in the known machine tool,sealing rings (O-rings) are inserted into two radially extending groovesof the percussion bolt, which seal the gap between the percussion boltand the inside of the tool holder.

[0003] In a percussive machine tool, the percussion bolt moves in theaxial direction, for example with a frequency of 65 to 85 Hz and anamplitude of 1 to 10 mm. In addition, the percussion bolt also moves inthe radial direction depending on component tolerances and a thermalexpansion of the materials. Under these circumstances, a seal insertedbetween the percussion bolt and the tool holder experiences a relativelyhigh amount of wear. The object of the invention, therefore, is toproduce a sealing ring, which experiences the least amount of wearpossible due to the motion of the percussion bolt and therefore assuresa high degree of impermeability over a long operation time of themachine tool.

ADVANTAGES OF THE INVENTION

[0004] The stated object is attained with the features of claim 1 byvirtue of the fact that the sealing ring has a number of sealing lipsthat rest against the percussion bolt and that at least on its lateralflank oriented toward the machine, the sealing ring is provided with oneor more radially extending recesses. This particular formation of thesealing ring lends the sealing lips a very high degree of flexibility sothat they can easily follow the axial and radial movements and thethermal expansion of the material without a large amount of wear andconsequently produce a reliable sealing of the percussion bolt in thetool holder.

[0005] Because one or more radially extending recesses are provided onthe lateral flank of the sealing ring oriented toward the machine, thepenetration of lubricant (oil or grease) from the transmission chamberinto the at least one recess causes the sealing lip oriented towardmachine to experience an increased pressure against the percussion boltand consequently increases the impermeability against an escape oflubricant from the transmission chamber of the machine tool. If thelateral flank of the sealing ring oriented toward the tool is alsoprovided with one or more radially extending recesses, this also lendsthe sealing lip oriented toward the tool a high degree of flexibility,allowing it to easily follow the axial and radial movements of thepercussion bolt as well as thermal expansions of the material andconsequently produces an effective seal of the transmission chamber ofthe machine tool against penetration of dust through the tool holder.

[0006] Advantageous modifications of the invention can be inferred fromthe dependent claims.

[0007] It is useful to provide both lateral flanks of the sealing ringwith one or more recesses in order, as mentioned above, to produce aseal that prevents both the penetration of dust and the escape oflubricant.

[0008] The sealing ring preferably has a cross-sectional form that issymmetrical with regard to a radial central plane thus preventing alaterally reversed insertion of the sealing ring.

[0009] A favorable adhesion of the sealing ring in the tool holder isachieved by virtue of the fact that the sealing ring is fitted with itsside oriented away from the percussion bolt into a radially extendinggroove in the tool holder.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

[0010] The invention will be explained in detail below in conjunctionwith an exemplary embodiment shown in the drawing.

[0011] The sole FIGURE of the drawing shows a longitudinal sectionthrough the front part of a rotating and hammering hand power tool,namely a percussive drill or a hammer drill. Freed of all parts of thehand power tool that are unnecessary for the explanation of theinvention, the drawing shows a tool holder 1 with a receiving bore 2 fora tool, for example a drill bit, a chisel, or the like. This tool holdertransmits a rotary motion from a drive mechanism that is not shown to atool that is inserted into it. A percussion bolt 3 is supported so thatit can move axially in the tool holder 1. A drive mechanism moves thispercussion bolt 3 back and forth axially in the tool holder 1 with afrequency of 65 to 85 Hz and an amplitude of 1 to 10 mm and transfersthis motion to a tool inserted into the tool holder 1.

[0012] A sealing ring 5, which encompasses the percussion bolt 3, isinserted into an annular groove 4 on the inside of the tool holder 1.The purpose of this sealing ring 5 on the one hand is to prevent anescape of lubricant (grease or oil) from the transmission chamber of themachine tool into the tool holder 1 and on the other hand to prevent thepenetration of dust from the tool holder 1 into the transmissionchamber. Fulfilling these high sealing requirements for the longestpossible operating time of the machine tool is problematic because thepercussion bolt 3 encompassed by the sealing ring 5 moves not only inthe axial direction, but also moves in the radial direction due tocomponent tolerances and thermal expansion of the materials. In order,even with these movements of the percussion bolt 3, to minimize the wearsusceptibility of the sealing ring 5 and therefore a slackening of itssealing action, the sealing ring 5 has two parallel sealing lips 6 and 7in the axial direction of the percussion bolt 3. The sealing lip 6oriented toward the interior of the machine seals the transmissionchamber against the escape of lubricant and the sealing lip 7 orientedtoward the tool produces a seal preventing the penetration of dust fromthe tool holder 1. The sealing ring 5 is thus formed so that separatesealing lips 6 and 7 perform the two sealing functions. The sealing ring5 can also have more than two sealing lips.

[0013] A rapid wear of the sealing ring 5 and therefore a loss ofsealing action can be counteracted by giving the sealing lips 6 and 7 ahigh degree of flexibility so that they can easily follow the axial andradial movements of the percussion bolt 3. A high degree of flexibilityof the sealing lips 6 and 7 is achieved by virtue of the fact thesealing ring 5 is provided with recesses 8 and 9 that extend radiallyaround the sealing ring on both of its lateral flanks above the sealinglips 6 and 7. This gives the sealing ring 5 a waist above the sealinglips 6 and 7, which make these sealing lips very mobile.

[0014] In contrast to the exemplary embodiment shown, a recess 8, 9 doesnot have to be provided on each lateral flank of the sealing ring 5.However, it is advantageous to provide at least one recess 8 on thelateral flank oriented toward the machine. This recess 8 would namelyhave the effect that lubricant from the transmission chamber of themachine tool could penetrate into this recess and, due to the pressureof the lubricant in the recess 8, the sealing lip 6 disposed underneathit would be pressed against the percussion bolt 3 with a greaterpressure.

[0015] The size and depth of the recesses 8 and 9 and depending on them,the thickness of the sealing lips 6 and 7, influence the flexibility ofthe sealing lips 6 and 7 and their contact force against the percussionbolt 3. The flexibility of the sealing lips 6 and 7 could be furtherincreased by providing not only one recess 8, 9 on each lateral flank ofthe sealing ring 5, but a number of radially extending recesses that areoffset from one another.

[0016] The ends of the sealing lips 6 and 7 resting against thepercussion bolt 3 are rounded so that they can slide as well as possibleagainst the moving percussion bolt 3.

[0017] The sealing ring 5 is preferably comprised of an elastomermaterial.

[0018] If, as shown in the drawing, a sealing ring 5 is used, which hasa cross-sectional form that is symmetrical with regard to a radialcentral plane 10, no particular insertion direction of the sealing ring5 needs to be maintained.

[0019] The region of the sealing ring 5 oriented away from thepercussion bolt 3 fills the annular groove 4 in the tool holder 1 overits entire width and rests flush in the groove. As a result, the outerregion of the sealing ring 5 has a high degree of stability and afavorable adhesion in the tool holder 1 so that the ring is securedagainst sliding in the axial direction and against rotating around thetool holder axis.

1. A hand power tool with a tool holder (1), which can be driven in arotary and percussive fashion and in which a percussion bolt (3) issupported so that it can move axially, in which the tool holder (1)contains at least one sealing ring (5) that encompasses the percussionbolt (3), characterized in that the sealing ring (5) has a number ofsealing lips (6, 7) that rest against the percussion bolt (3) and thatthe sealing ring (5), at least on its lateral flank oriented toward themachine, is provided with one or more radially extending recesses (8,9).
 2. The hand power tool according to claim 1, characterized in thatthe sealing ring (5) is provided with one or more radially extendingrecesses (8, 9) on each of its two lateral flanks.
 3. The hand powertool according to claim 1 or claim 2, characterized in that the sealingring (5) has a cross-sectional form that is symmetrical in relation to aradial central plane (10).
 4. The hand power tool according to claim 1,characterized in that with its side oriented away from the percussionbolt (3), the sealing ring (5) is fitted into a radially extendinggroove (4) in the tool holder (1).